Retinoic acids (RA) are derivatives of vitamin A that have both diverse and essential actions in developmental and cellular differentiation processes. The RA signal is transduced in vivo by the RAR and RXR receptor families of proteins, all of which are ligand-dependent transcription factors belonging to the nuclear receptor family. The GRP1-associated scaffold protein (GRASP) is encoded by a novel, RA-induced gene that was recently cloned by these investigators. The long-term goal of this laboratory is to elucidate the function of, and mechanistic basis for, GRASP action in the RA signaling pathways. To advance toward this goal, the objectives of this proposal are: (1) to identify and functionally characterize the components of cellular complexes containing GRASP, and (2) to determine the role of GRASP in cellular signaling pathways and in mediating the well characterized effect of RA during F9 EC cellular differentiation. These objectives will be achieved in the context of the investigators' central hypothesis: GRASP and associated proteins play key roles in the signaling pathways underlying growth inhibition and cellular differentiation induced by RA. This central hypothesis will be tested and overall objectives of this proposal will be accomplished by achieving 3 specific aims: (1) to identify the component proteins of cellular GRASP complexes in F9 EC cells (collaboration with the Deinzer laboratory), (2) to elucidate the cellular function of GRASP (collaboration with the Greenwood laboratory), and (3) to determine the function GRASP in F9 EC cells (collaboration with the Metzger laboratory from the Institut de Genetique et de Biologique Moleculaire et Cellulaire [IGBMC] in Illkirch, France). This research will have significant, positive effects on human health because the proposed studies focus on determining the molecular basis of action of vitamin A, an important therapeutic agent in the management of numerous human diseases. As a direct outcome of this work, the investigators expect to provide an enhanced understanding of the effects of RA on molecular and cellular levels, which should facilitate the development of new therapeutic strategies in the treatment of proliferative diseases in humans, such as cancer. A second beneficial aspect of this work is that fundamentally new knowledge will be gained that is expected to advance the understanding of the RA signaling mechanisms implicated in cellular differentiation, growth inhibition and homeostasis.